Abbreviations3GPP3rd generation Partnership ProjectAMAcknowledge ModeCDMACode Division Multiple AccessCell_DCHCell_Dedicated ChannelCell_PCHCell_Paging ChannelC-RNTICell RNTIDLDownlinkEDGEEnhanced Datarate for GSM EvolutioneNBEvolved NodeBE-DCHEnhanced Dedicated ChannelE-FACHEnhanced FACHE-RACHEnhanced RACHE-RNTIE-DCH RNTIE-UTRAEvolved Universal Terrestrial Radio AccessFACHForward Access ChannelGPRSGeneral Packet Radio ServiceGSMGlobal System for Mobile CommunicationH-RNTIHS-DSCH RNTIHS-DSCHHigh Speed Downlink Shared ChannelHSPAHigh Speed Packet AccessLTELong Term EvolutionLTE-ALTE AdvancedNodeBBase station of UTRANPDUPacket Data UnitRACHRandom Access ChannelRBRadio BearerRLCRadio Link ControlRNCRadio Network ControllerRNTIRadio Network Temporary IdentifierRRCRadio Resource ControlTSTechnical SpecificationUEUser EquipmentULUplinkURA-PCHUMTS Radio Access_Paging ChannelUTRANUniversal Terrestrial Radio Access NetworkWiFiWireless Fidelity
3GPP release 7 introduced the enhanced FACH and release 8 introduced the enhanced RACH feature, thus allowing UE and UTRAN to use HSPA channels (in Cell_FACH state) in uplink and downlink directions to improve end user experience. If both the UE and the UTRAN support E-FACH (release 7) or E-RACH/E-FACH (release 8), then UTRAN provides the corresponding Radio Bearer (RB) Mapping for each established Radio Bearer and other parameters to the UE, to allow user plane to work in Cell_FACH state. UTRAN also provides corresponding RLC configuration for E-RACH in UL or E-FACH in DL for the data RB and the transport channel configuration in a dedicated RRC message.
UTRAN is allowed to perform further state transitions from Cell_FACH to Cell_DCH/Cell_PCH/URA_PCH, all of them being in the RRC connected mode. Details on these states and their transitions are given in 3GPP TS 25.331. FIG. 1, taken from 3GPP TS 25.331, V8.24.0, shows the states and their transitions for 3GPP release 8, section 7.1, and also their transitions to idle mode (shown at the bottom of FIG. 1) and inter-RAT transistions to/from E-UTRA, GSM, and GPRS. The RRC connection is defined as a point-to-point bi-directional connection between RRC peer entities in the UE and the UTRAN characterised by the allocation of a U-RNTI. A UE has either zero or one RRC connection.
The Forward Access Channel (FACH) is a downlink transport channel that carries control information to terminals known to be located in the given cell. This is used, for example, after a random access message has been received by the base station. It is also possible to transmit packet data on the FACH. There may be more than one FACH in a cell. The FACH does not use fast power control, and the messages transmitted need to include in-band identification information to ensure their correct receipt. The FACH is a downlink channel with low rate payload.
RACH is a shared channel that is used by terminals to access the access network especially for initial access and bursty data transmission.
According to 3GPP TS 25.331, when a user initiates a call an RRC CONNECTION REQUEST message is sent by the UE to the network to trigger the establishment of a radio resource control connection. The network then assigns radio resources to the UE and sends an RRC CONNECTION SETUP message to direct the UE to properly configure its signaling radio bearers. After the UE has configured its radio resource control connection, the UE sends an RRC CONNECTION SETUP COMPLETE message to the network. After the network receives the message that the radio resource control connection is properly configured, the network sends a RADIO BEARER SETUP message to direct the UE to properly configure its user radio bearers. Once the user radio bearers are properly configured, the UE sends a RADIO BEARER SETUP COMPLETE message to the network. Because this message is sent in Radio Link Control (RLC) acknowledgement mode, the network sends an RLC protocol layer ACK to the UE upon reception of the RADIO BEARER SETUP COMPLETE message.
If a radio link failure, such as a signal fade or excessive signal noise, occurs during or after the RRC layer in the UE submits a RADIO BEARER SETUP COMPLETE message to its lower layers for transmission to the network, the network will not receive the RADIO BEARER SETUP COMPLETE message and the network will not send an RLC layer ACK. Upon radio link failure, the UE will send a CELL UPDATE message with a cause of “radio link failure.” Because the network did not receive a RADIO BEARER SETUP COMPLETE message from the UE, the network will assume that the UE failed to properly configure its radio bearers in accordance with the earlier RADIO BEARER SETUP message from the network. This could lead to the network and the UE getting out of sync with respect to the configurations used at their respective ends-eventually leading to a call drop.
US 2006/246883 discuss a case of cell reselection during RLC reconfiguration. According to this prior art, either the previous or the new RLC configuration is used after cell update from a first cell to a second cell by both the UE and the network. It does not consider a case of different capabilities in the first cell and the second cell.